Book : Botany
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Posted by: CHELSEA
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Compositate (Asteraceae)

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Introduction

Asteraceae or Compositae (commonly referred to as the aster, daisy, composite, or sunflower family) is an exceedingly large and widespread family of flowering plants (Angiospermae). The family has more than 23,600 currently accepted species, spread across 1,620 genera (list) and 13 subfamilies.

Properties

Distribution: The members of the family are found all over the worls(cosmopolotian), most of them are found in the tropical regions. Habit and Habitat: Annual or perenneal herbs or under shrubs or shrubs, rarely trees or climbers. Many are xerophytes or mesophytes, a few are aquatic. Root: Usually, tap and branched, sometimes adventitious. In Helianthus, the roots are modified into tubers. Stem: Erect or postulate, rarely climbing, herbaceous or woody, solid or fistular, sometimes spiny e.g. Sonchus, sometimes modified into tuber e.g. Helianthus, some contains latex e.g. Sonchus or oil glands. Leaf: Radical, cauline or ramal, usually alternate, sometimes opposite and rarely whorled, simple or compound, estipulate, glabrous or hairy; entire or serrate or lobbed, apex acute or obtuse, reticulate venation. Inflorescene: Racemose, head or capitulum with an involucres of bracts; rarely in spike. Flower: Sessible, bracteable or ebracteate, two kinds of flowers are found in inflorescence, towards the center are tubular flowers called disc florets and towards the periphery of captulum are liguate flowers called ray florets. Ray florets: Sessile, bracteates or ebracteate, ireegular or zyomorphic, ligulate, incomplete, unisexual or neuter, pentamerous, epigynous. Calyx: Sepals-2-5, represented by scales or hairy, pappus, velvate, superior. Corolla: Petals-3, gamopetalous, ligulate, velsate superior. Androecium: Absent Gynoecium: Bicapellary, sycarpous, ovary inferior, unilocular containing a single anatropous ovule, basal placentation, style long and slender, stigma bifid. Disc floret: Sessile, bracteate or ebracteate, actinnomoprphic, incomplete or complete, bisexual, pentamenous, tubular, epigynous. Calyx: Sepals-2-5, represented by scale or hairy peppus, aestiration, superior. Corolla: Petals-5, gamopetalous, tubular, actinomorphic, valvare aestivation, superior Androecium: Stamen-5, syngenesious epipetalous, anthers bicelled, basified, introse, supenor Gynoecium: As in ray floret i.e. bicapellary, syncarpous, ovary inferior, unilocular containing a single anatropous ovule, basal placentation, style long and slender, Stigma bifid. Fruit: Cypselu Seed: Exalbuminous

Classification

Kingdom: Plantae Sub-kingdom: Phanerogamae Division: Angiospermae Class: Dicotyledoneae Sub-class: Garropetalae Series: Inferae Order: Asterobs Family: Compositae (Asteraceae)

Economically important plants

Helianthus annus (sunflower): oil yielding Tagetes patula (Mangold): medicinal plants Lactuca satira (Lettuce): vegetable Dahlia variabillis: ornamental

Diagnostic features of family Compositae (Asternaceae)

Stem: hairy and with latex or oil ducts 

Inflorescene: head or capitulum having involucres of bract 

Flowers: Sessile called florets, two types of flowers ; ray florets and disc florets 

Florets: tubular or ligulate, epigynous 

Calyx: represented by sales, bristles or pappus 

Corolla: 3-5, gemopetalous, toothed 

Stamens: -5, syngenesioud and epipetalous in disc floret Gynociem: bicapilarry, ovary inferior, based placentation 

Fruit: Cypsela


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